Balance comprising knife edge bearings



Nov. 26, 1968 WEICKHARDT 3,413,044

BALANCE COMPRISING KNIFE EDGE BEARINGS Filed Jan. 10, 1967 2 Sheets-Sheet 1 INVENTOR LUDWIG WEICKHARDT BYOW Nov. 26, I968 I WEICKHARDT 3,413,044

BALANCE COMPRISING KNIFE EDGE BEARINGS Filed Jan. 10, 1967 2 Sheets-Sheet 2 Fig.4

INVENTOR LUDWIG WISICKHARDT wafmfaaz United States Patent 3,413,044 BALANCE COMPRISING KNIFE EDGE BEARINGS Ludwig Weickhardt, Gottingen, Germany, assignor t0 Sartorius-Werke G.m.b.H. (und vormals Goettinger Praezisionswaagenfabrik G.m.b.I-I.)

Filed Jan. 10, 1967, Ser. No. 608,406 Claims priority, application Germany, Jan. 28, 1966, S 101,680 9 Claims. (Cl. 308-2) ABSTRACT OF THE DISCLOSURE This disclosure relates to a balance which comprises knife edge bearing assemblies consisting of two spaced apart parts, each of which comprises a knife edge memher and a V-bearing. The knife edge members and V-bearings are engageable in a line of contact. The invention provides torsionally elastic means which elastically oppose a relative movement of said knife edge members and V- bearings in the direction of said line of contact so that the danger of damage due to impact between the knife edge members and other parts of the balance in the direction of said line of contact is minimized and an action of frictional torque on said bearing assemblies is prevented.

Description This invention relates to a device which is provided at a bearing assembly of a balance and serves to substantially prevent a longitudinal movement between the knife edge members and the V-bearings cooperating therewith, which knife edge members and V-bearings are provided in each of two spaced apart parts of the bearing assembly so that the lines of contact of the two parts of the bearing assembly are aligned. In this case the term line of contact relates to the line where a knife edge member contacts its V-bearing in the operative condition of the balance. This line of contact is a straight line in the present case. The term longitudinal movements will be used to describe movements in the direction of the line of contact. It will be understood that such longitudinal movements must be substantially prevented in order to ensure that the knife edge member does not run off the V-bearing. Even smallor longitudinal movements would be detrimental because a pointer, which is secured to the balance beam, could chafe on.a stationary scale, or a scale which is mounted on the balance beam and intended to be projected could be displaced within an optical system so that the projected image gets out of focus.

It has previously been attempted to eliminate this problem by grinding the end faces of the knife edge member in such .a manner that they form together with the knife .edge a pointed tip, which is aligned with the line of contact. The longitudinal movement of the knife edge member was limited by abutment plates of hardened material, which faced the pointed tips.

It has been found that the small, but yet disturbing frictional torque is created in operation by the contact between a pointed tip and an abutment plate. This frictional torque resulted in an undesired reduction of the sensitivity of the balance, more specifically in a hysteresis error. It has been attempted to reduce the friction by the use of hardened steel balls as abutments for the knife edge members.

When the balances were used and particularly when they were being transported, the pointed tips of the hardened knife edge members were often damaged by impinging on the abutment plates or balls. Such damage resulted i a much increased frictional torque. The same result was 3,413,044 Patented Nov. 26, 1968 observed when the impinging pointed tip of the knife edge member struck a recess into the abutment plate.

It is an object of the present invention to provide a bearing assembly which is inherently 'free of frictional torque and in which a longitudinal movement between the knife edge members and V-bearings is entirely prevented or is minimized so that any damage due to impact is prevented. According to the invention, this is accomplished in that elastic elements are provided between the two parts of the bearing assembly, which elements have an inherent elasticity in the direction of the rotational movement enabled by the bearing assembly and are inherently elastic in the direction of the line of contact of such bearing assembly and/ or are mounted for elastic movement in this direction, the axes of the elastic elements lie in said line of contact when said balance is in an operative condition, mutually adjacent ends of the resilient elements are connected to one carrying member and mutually remote ends of the resilient elements are connected to another carrying member of the balance, which carrying members carry the knife edge members and V-bearings of the bearing assembly, respectively.

The elastic elements may be compression springs or tension springs, which have such constants and such a relative initial tress that damage to the ends of the knife edge members is impossible even when substantial shocks occur in transit. The springs enable a rotation of the knife edge members relative to the V-bearings without friction. The twisting of the springs results only in a slight restoring, which is superimposed on the anyway required restoring torque of the balance beam and is not detrimental.

In a development of the invention, the elastic elements may be torsion strips or torsion wires. The use of such torsion strips or wires reduces the cost of the arrangement. To simplify the language, only the term torsion strips will be used hereinafter in such a sense that it includes also torsion wires. In addition to the torsional deformation which is required, the torsion strips may be elastically elongated to a slight extent. This is important because the knife edges must be lifted from the V-bearings when the balance is to be locked. Even when the balance is locked, the torsion strips hold the knife edge members in a correct position relative to the V-bearings. As the torsion strips are slightly stressed in their longitudinal direction when the balance is being locked, the restoring force tending to maintain the torsion strips in their intermediate position is larger in the locked condition of the balance than in its operative condition. This is desirable because the balance is required to withstand particularly high shock stresses when in a locked condition.

In a preferred embodiment, the elastic elements constitute one-half portions of a continuous torsion strip, which is connected at its ends to one of the carrying members and in the middle to the other carrying member. The use of a continuous torsion strip further reduces the cost of the assembly. In this case, it will be particularly desirable if the middle of the torsion strip is connected to the same carrying member as the knife edge members. As the knife edge members are usually secured to the balance beam, only the smaller part of the mass of the torsion strip assembly need to be connected to the beam.

If the elastic elongation of the torsion strip or torsion strips is not sutficient to enable the locking operation or it is not desired to utilize the elastic elongation of the strips for this purpose, the ends of the torsion strip or strips may be connected to one of the two carrying members by means which are elastic in the longitudinal direction of the torsion strips. These elastic connections will then enable the torsion strips to yield sufficiently during the locking operation. On the other hand, said elastic connecting means are dimensioned so as to resist even very high shock stresses without causing an impact of the ends of the knife edge members.

Illustrative embodiments of the invention will be described hereinafter with reference to the accompanying drawings, in which FIG. 1 is a simplified side elevation showing a known balance, which has a pan disposed above the beam. In this balance, a spring assembly according to the invention is provided at the fulcrum bearing of the balance beam as well as at the nose bearing for the pan carrier.

FIGS. 2 to 4 are fragmentary views taken in the direction of the arrow A in FIG. 1 and showing in elevation, partly in section, a spring arrangement according to the invention, which arrangement is provided at the nose bearing of the balance and comprises a continuous torsion strip, cylindrical tension springs and cylindrical compression springs, respectively.

A bearing bracket 1 is secured to a base plate and l carries a V-bearing 2, which belongs to a fulcrum bearing. The V-bearing 2 supports the knife edge member 3, which is secured to the balance beam 4. The longer lever arm of the balance beam is provided with a microscale 5. An image of this scale is projected onto a ground glass screen. A knife edge member 6, which forms part of a nose bearing, is secured to the short arm of the beam. A V-bearing 8 is secured to a pan carrier 7 and rests on the knife edge member 6. Rods 9 depend from the pan carrier and are connected by links 10 to bearing brackets 11, which are secured to the base plate so that the pan carrier 7 is vertically guided in known manner.

As is shown in FIG. 2, the nose bearing comprises lefthand and right-hand parts. Each of said parts comprises a V-bearing 8. As is shown in FIG. 2, the knife edge members 6 are the end portions of a single member 6'. A ternatively, two separate knife edge members may be used.

Angle brackets 11 are secured to the pan carrier 7. A torsion strip 13 extends over two leaf springs 14, which have inturned lower end portions, and is screw-connected to the angles 11 and clamped against the same by respective washers 15. In their inoperative condition, the leaf springs are curved outwardly so that they are prestressed when the torsion strip has been secured in the position shown in FIG. 2. The intermediate portion of the torsion strip 13 is twisted through 90 and secured to the middle of member 6 by means of an angle bracket 17. The torsion strip is arranged so that its longitudinal axis is longitudinally aligned with the line of contact.

The torsion strip is detachably mounted at its three fixing points so that the blance can be knocked down without destruction of the torsion strip assembly.

Instead of a single torsion strip, as shown in FIG. 2, two separate torsion strips may be employed, which have adjacent ends that are separately secured to the angle bracket 17. This arrangement involves a somewhat higher structural expenditure. The arrangement may be reversed in that the leaf springs 14 are connected at closely spaced points to the middle portion of member 7 or 6 and angle brackets serve for a rigid connection of the mutually remote spring ends to the other carrying member. It will be desirable, however, if the elements which have a smaller mass are attached to member 6, which is connected to the balance beam 4.

In the embodiment shown in FIG. 3, a longitudinal movement between the knife edges and V-bearings is opposed by two cylindrical tension springs 22. Rigid angle brackets 24 are secured to the pan carrier. A rigid mounting 26 is fixed to the middle of member 6'. The tension springs 22 are connected under initial stress between the mounting and the angle brackets in such a manner that their longitudinal axes are longitudinally aligned with the line of contact.

In the embodiment shown in FIG. 4, cylindrical compression springs 30 rather than tension springs are used. Sleeves 28 are connected to the angle brackets 24- and the mounting 26 and receive the compression springs under initial stress. The longitudinal axes of the springs lie again in the line of contact.

What is claimed is:

1. A balance, which comprises first and second carrying members, and

a bearing assembly connecting said carrying members for rotation relative to each other, said bearing assembly comprising knife edge members carried by one of said carrying members and V-bearings carried by the other of said carrying members, said knife edge members being adapted to contact said V-bearings along a line of contact, said bearing assembly consisting of spaced apart first and second parts, each of which comprises one of said knife edge members and one of said V-bearings,

said balance further comprising first and second elastic elements,

said first elastic element having one end which is connected to said first carrying member at said first part of said bearing assembly,

said second elastic element having one end which is connected to said first carrying member at said second part of said bearing assembly,

each of said elastic elements having another end, which is connected to said second carrying element intermediate said first and second parts of said bearing assembly,

said elastic elements being torsionally eastic about said line of contact and longitudinally elastic in the direction of said line of contact when said knife edge members contact said V-bearings along said line of contact.

2. A balance as set forth in claim 1, in which said elastic elements comprise means which are torsionally and longitudinally elastic.

3. A balance as set forth in claim 1, in which said elastic elements comprise means which are torsionally elastic and means which are longitudinally elastic.

4. A balance as set forth in claim 1, in which said elastic elements comprise torsion strips.

5. A balance as set forth in claim 4, in which said elastic elements comprise torsion wires.

6. A balance as set forth in claim 1, in which said first and second elastic elements comprise one-half portions of an integral torsion strip, which is connected at its ends to said first carrying member and in the middle to said second carrying member.

7. A balance as set forth in claim 6, in which said knife gdge members are carried by said second carrying mem- 8. A balance as set forth in claim 6, in which said first and second elastic elements comprise means which connect the ends of said torsion strip to said first carrying member and which are elastic in the longitudinal direction of said torsion strip.

9. A balance as set forth in claim 1, in which said first and second elastic elements comprise first and second torsion strips and connecting means between ends of said torsion strips and one of said carrying members, said connecting means being elastic in the longitudinal direction of said torsion strips.

References Cited UNITED STATES PATENTS 1,741,737 12/1929 Ring 3082 2,611,659 9/1952 Hadley. 2,721,770 10/ 1955 Wagner 3082 FOREIGN PATENTS 58,734 3/1954 France. 367,638 4/ 1963 Switzerland.

EDGAR W. GEOGHEGAN, Primary Examiner.

L. L. JOHNSON, Assistant Examiner. 

